1. Field of the Invention
The present invention relates to an angular rate detecting device for detecting angular rate of an object using a Coriolis force.
2. Description of the Related Art
Devices related to the present invention are disclosed, for example, in Technical Digest of the 16th Symposium, 1988, pp. 37-40, Japanese Patent Publication Laid-Open No. HEI 10-103960, and Transducer of IEEE, 1997, pp. 1129-1132. An angular rate detecting device as described in these publications is composed of an oscillation portion connected to a substrate via a supporting member and oscillatable over the substrate in directions of mutually perpendicular X and Y axes, a drive portion on the substrate causing the oscillation portion to oscillate in the direction of the X-axis, and a detection portion on the substrate detecting oscillation of the oscillation portion in the direction of the Y-axis. Based on oscillation of the oscillation portion in the direction of the Y-axis, the angular rate detecting device detects an angular rate effective around a Z-axis which is perpendicular to both the X-axis and the Y-axis, with the oscillation portion oscillating in the direction of the X-axis.
The Transducer of IEEE publication discloses an oscillation portion composed of a rectangular frame and an oscillator. The frame is connected to the substrate through drive beams serving as supporting members so that the frame can oscillate in the direction of the X-axis. The oscillator is disposed within the frame over the substrate, and connected through detection beams serving as supporting members so that the oscillator can oscillate with respect to the frame in the direction of the Y-axis. In this construction, the drive portion drives the frame in the direction of the X-axis and causes the oscillator to oscillate with respect to the substrate in the direction of the X-axis. Further, the detection portion detects oscillation of the oscillator with respect to the substrate in the direction of the Y-axis to prevent undesirable external driving forces acting in directions other than that of the X-axis from being transmitted to the oscillator. Therefore, the angular rate around the Z-axis makes it easy for the oscillator to oscillate in the direction of the Y-axis, maintaining a high precision in detecting angular rate. According to what is disclosed in Japanese Patent Publication Laid-Open No. HEI 10-103960, in order to prevent part of a drive signal causing the oscillation portion to oscillate in the direction of the X-axis from leaking out in the direction of the Y-axis (such leak will be referred to hereinafter as cross talk) and acting as noise, a correction portion for causing the oscillation portion to oscillate in the direction of the Y-axis is provided to cause the oscillation portion to oscillate in the direction of the Y-axis by an amount large enough to counterbalance the cross talk.
However, in this kind of angular rate detecting device, the oscillation portion (the oscillator) cannot be caused to oscillate stably in a desired direction (the direction of the X-axis) with high precision because of not only a detection error of angular rate resulting from the cross talk but also processing inconsistency of the oscillation portion (the oscillator), the drive portion, the frame and the beams. Also, the oscillator cannot oscillate stably in a desired direction (the direction of the Y-axis) with high precision in accordance with a Coriolis force. Thus, the precision in detecting angular rate deteriorates.
Also, in an angular rate detecting device belonging to the aforementioned publications wherein the rectangular frame is connected to the substrate through the drive beams and the oscillator is connected to the inside of the frame through the detection beams, if the substrate is deformed owing to external factors such as a change in temperature, or an external force, etc., the frame and the drive beams are also deformed in accordance with the deformation of the substrate. Hence, an internal stress is generated in the drive beams, so that the non-linearity of the spring constant of the drive beams increases or the deformation amount of the drive beams is restricted. As a result, the oscillator cannot be caused to oscillate stably in a desired direction (in the direction of the X-axis) with high precision, and there is also caused a problem of deterioration of precision in detecting angular rate. Moreover, in this type of angular rate detecting device, a pair of drive beams are provided at opposed ends of each of the opposed sides of the frame. Therefore, the stress applied to one of the beams becomes too large, so that the non-linearity of the spring constant of the drive beams increases or the deformation amount of the drive beams is restricted. Thus, the oscillator cannot be caused to oscillate in a desired direction (the direction of the X-axis) with good stability, high precision and a great amplitude, so that the precision in detecting angular rate deteriorates.
Furthermore, in the angular rate detecting device belonging to the aforementioned publications, the oscillation and cross talk of the oscillator in the direction of the Y-axis generated in accordance with the Coriolis force are also inputted to the substrate through the frame and the beams. Then, the counter reaction against the inputted oscillation is reversely inputted to the oscillator from the substrate through the frame and the beams. The oscillation inputted to the oscillator becomes a cause of noise obscuring the angular rate to be detected. Therefore, if the oscillation and cross talk of the oscillator generated in accordance with the Coriolis force in the direction of the Y-axis become large, the precision in detecting angular rate deteriorates.